Machine table feed control system for electrolytic grinding machines

ABSTRACT

In electrolytic grinding machines where a working voltage is applied between grinding wheel and workpiece, the feed speed of the machine table is very important, and an inappropriate speed inconsistent with prevailing working conditions would result in the reduction of working efficiency and working precision and a degradated surface roughness, as well as being prone to shortcircuit between the grinding wheel and workpiece. In this specification, a machine table feed control system for automatically controlling the feed speed of the machine table to an optimum speed consistent to prevailing working conditions is disclosed.

Suzuki et a1.

[ Aug.- 28, 1973 Koike 204/225 X MACHINE TABLE FEED CONTROL 3,684,6828/1972 SYSTEM FOR ELECTROLYTIC GRINDING MACHINES Primary Examiner-JohnH. Mack Assistant Examiner--D. R. Valentine [75] Inventors z rgzzrttgtgvgg' Attorney-Paul M. Craig, Jr. et a1. Japan ABSTRACT [73]Assignee: Hitachi, Ltd., Tokyo, Japan [57] g In electrolytic grlndmgmachines where a working volt- [22] Fled: 1972 age is applied betweengrinding wheel and workpiece, 2 App] 240 031 the feed speed of themachine table is very important, a and an inappropriate speedinconsistent with prevailing [30] I r i Applfcatlon r i a a workingconditions would result in the reduction of Apr. 2, 1971 Japan..46/l9695 working efficiency and working precision and a de- 4 gradatedsurface roughness, as well as being prone to g short-circuit between thegrinding wheel and worka [58] Field of Search 204/224 M, 225, 129.2,

- 204 129, 223 In this specification, a machine table feed controlsystem for automatically controlling the feed speed of [56] ReferenceCited the machine table to an optimum speed consistent to I prevailingworking conditions is disclosed.

3,288,693 11/1966 Livshits 204/224 M X 2 Claims, 8'Drawlng Figures3,442,785 5/1969 Easton 204/224 M 3,650,938 3/1972 O1ton et a1 204/225 XY /,7, 2 I8, 1 PULSE O l AMPLIFIER MUL 4 2 5 VIBRATOR POWER 5 6 SOURCE v3 AMPLIFIER 5/. mm

1 /2 /3 SHUIVT 2 I5 I6 J, 1 1

AMPLIFIER SL/CER AMPLIFIER SLICER PATENTEBmzams v 3.155129 Y I W! 1 0f 4/7, 1 1\ PULSE OlY/E-SHOT I/ M m- 4 I AMPLIFIER WBRATOR POWER 5 SOURCE 31 AMPL/F/ER SL/CER l I 2 A3 SHUNT J7 ,6}

AMPLIFIER SL/CER AMPLIFIER 31/65? PATiNtimuczems 1155129 SHEEI 2 0f 4PULSE ONE SHUT AMPL IF IE7? 3L /CE/? AMPLIFIER 8L ICE 20 AMPLIFIERSL/CER J This invention relates to machine table feed systems forelectrolytic grinding machines.

In the usual electrolytic grinding machines, the machine table feedspeed has been preset to constant value on the basis of material ofworkpiece, depth of I cut, shape of finish and other working conditions;and

manually adjusted when sparking occurs during'the grinding process.

With the manual control of the feed speed, however, sufficiently quickresponse cannot be expected. There.- fore, the grinding wheel wearsquickly, and theprecision is inferior. In addition, when a workpiece,is-a welding of silver soldering were done in a part of workpiece, theworking efficiency is very inferior since the feed speed is preset onthe basis of a material of the slowest electrochemical dissolutionspeed.

There are some spark detection methods which are ulitized in othermachines. In one such method. a photoconductive element for thedetection of spark'is used, in another method variation of input powersupplied to a grinding wheel drive motor is detected, in'a furthermethod a variation in working current is detected through a shunt, andin a still further method the shaft torque is detected. These methods,however,- cannot be applied to the electrolytic grinding where thegrinding;

nal shaping circuit to shape the spark signal output source thedetecting circuit for each predetermined pulse period irrespective ofthe amplitude of the working current, a memory to phase modulatethe'output' signal of the spark signal shaping circuit and store themodulated information, and a speed control circuit to control the speedof a feed motor in accordance with the output content of the memory. Inthe spark signal shaping circuit, the spark signal output of thedetecting circuit is processed to remove noise components, and theresultant signal free from noise is shaped on the basis of a pulsesignal, which is derived by modulating a soruce waveform and at apredetermined pulse frequency. When the working current is low, a signalfrom a shunt or a resonant circuit is processed to obtain the sparksignal, while when the working current is high the spark signal isobtained through a separate resonantcircuit. The spark signal thusobtained and-which is shaped for each predetermined pulse period issmoothed through the memory into a gradually varying waveform, which iscoupled to the gate of an SCR connected to a power source feeding amachine table feed motor so as to control the effective power suppliedto the motor, thereby controlling the motor speed.

The accompanying drawings show preferred embodi ments of the invention,and in which:

FIG. 1 is a schematic representation of a detecting.

circuit;

FIG; 2'is a schematic representation of a spark signal shapingv circuit;I

FIG. 3 I518. timingichart showingwaveforms occurring at :variouspartsof'the circuit of FIG. 2;

FIG 4 is a schematic. representation of another; example-of the sparksignal shapingcir'cuit;

FIG. Sis a schematicarepresentation 'of'azspeedcontrol circuit; and

FIGS. 6m 8 are timingcharts showing waveforms occuring. at various partsof the circuit .orrro. 5.

FIGS. l to8 showan embodiment of the electrolytic grinding machinetabletfeed control system according to theinvention.

Referringto FIG. 1, reference numeral :1 generally designates adetectingcircuit. A. grounded lmachine table2 carries a workpiece 3. set thereon;Thetable. and a grindingwheel '5 of graphiteor the like-areconnected toa powersource- 4; to which a: resonant circuit of cawave-rectifiedd-cvoltageas shown at iA-= (FIG. 3).

FIG. 2 shows the "above detecting .circuitl together witha spark signalshaping-circuit generally designated at The working current from: the:power source :4 is shunted atlashunt ll; The output terminal 9' isconnectedthrough anamplifier-lZand a slicer l3.'to oneinput terminal ofan AND gate 14. The'shunt *1 l :is cou. pled through another amplifierl5 and another slicer 16 to another input terminal of the AND gate-.14;Further;

the power source 4 at the side thereof connected to the.

grinding wheel 5 is also connected through'a pulse amplifier l7 and aone-shot multi-vibrator l8- to athird input terminal of theAND gate. 14.Theoutput of the AND gate l4'is coupled to an-0R'gatex19. .The output ofthe one-shotmulti-vibrator l8-also constitutes an input to :another ANDgate 20. The shunt ll'is'also coupled through a further amplifier'Zl anda further slicer 22 to the other input terminal of the ANDgate 20.- The:AND gate 20 isconnected .to theOR gate 19 which is connected :to anoutput terminal 23.

The. slicer 13 receiving. the amplified spark signal provided an outputsignal having awaveform as shown at C (FIG. 3) and constituting an'inputto-the AND gate 14. Since the working voltage A" is differentiated'through an SCR system, the output C contains acorresponding series ofpulses at a constant repetition frequency. Also, in the initial workingstage where there are fluctuations in theelectrolyte and the process arenot stabilized yet, high frequency'current fluctuations are caused andconstitute noise added to the spark signal waveform a. v

Since other components than the sparksignal. waveform a are undesired,they are removedfrom the out put C. This is done .at the AND gate 14.More particularly,the one-shot multi-vibrator "18 produces output ofwaveform B (FIG. 3) fromthewaveforrn A, whereby the differential pulsecomponentis removed. The high frequency noise is removed byarranging-such that the output E(FIG. 3) of the slicer l6=willnot-beraised to ahigh level until a .voltage D(FIG. 3) provided :bytheamplifier 21 detecting mean shunted workingcurrent from the shunt llexceeds a predetermined leve. In this manner, the AND gate 14 providesoutput waveform G(FIG. 3) solely consisting of the spark signal waveforma during the stabilized process.

During the initial working stage during which the working current islow, the spark waveform can be detected through the shunt. In thisembodiment, the slicing level for amplifier 21 and slicer 22 is adjustedsuch that the AND gate 20 receiving the afore-mentioned waveform B andthe output of the slicer 22 provides output signal I-I (FIG. 3). Thespark signals H and G during the initial non-stabilized stage and thesubsequent stabilized stage are combined at the OR gate 19 to produceresultant waveform I (FIG. 3) available at the output terminal 23. Inthis manner, the spark signal a freed from any noise component can beobtained for the entire process.

FIG. 4 shows another embodiment of the invention. This embodiment is thesame as the preceding embodiment insofar as it includes resonant circuit8 and shunt 11 for the detection of the spark waveform. In thisembodiment, however, another resonant circuit consisting of a primaryseries circuit of capacitor 41 and coil 42 and a secondary parallelcircuit of coil 43 and capacitor 44 and generally designated at E isprovided in parallel with the resonant circuit 8. With this arrangement,during the initial low working current stage the resonant circuit 4 5detects the signal, which is then coupled through amplifier 21 andslicer 22 to the AND gate 20. This enables the obtaining of superiordetection of spark waveforms during the small working current stage aswell as during the large working current stage.

The other parts are the same as in the preceding embodiment, so they aredesignated by the same reference numerals as in FIG. 2.

FIG. shows the detecting circuit l and spark signal shaping circuit 1 0together with a speed control circuit generally designated at 24.Connected across one secondary coil of a source transformer 25 through athreeterminal thyristor 26 (hereinafter referred to as SCR) is a machinetable feed motor 28, to which a tachogenerator 27 is coupled. The outputterminal 23 is connected to a flip-flop 29 and to a reversible counter30, to which the output of the flip-flop 29 and a pulse generator 31 arealso coupled. The secondary of the source transformer 25 is alsoconnected to a pulse amplifier 32, whose output is connected to theflip-flop 29, a free counter 33, an oscillator 34 connected to the freecounter 33 and to another flip-flop 35. The outputs of the free counter33 and reversible counter 30 are coupled to a coincidence circuit 36,whose output is coupled to the flip-flop 35, whose output is in turncoupled through a d-c signal circuit 37 to a differential amplifier 38,to which a pre-set voltage circuit 39 is connected. The output of thedifferential amplifier 38 is coupled through an SCR igniting circuit 40to the gate of the SCR 26. The output of the tachogenerator 27 is fedback to the differential amplifier 38.

The output I solely consisting of the spark signal a appearing at theoutput terminal 23 sets the flip-flop 29 to provide an additionalcommand to the reversible counter 30 so as to cause the countingoperation of the counter. The content of the reversible counter 30 is asshown at S in FIG. 8. When the spark signal a vanishes, the pulseamplifier 32 generates a pulse signal I synchronized with the sourcefrequency, whereupon the flip-flop 29 provides a subtraction command tothe reversible counter 30 for subtraction of a train of pulses providedfrom the pulse generator 31 and having an extremely long pulse period ofabout one pulse per 10 seconds. The pulse signal J from the pulseamplifier 32 is also coupled to the oscillator 34 which provides clockpulses R (FIG. 7) at a high pulse frequency to the free counter 33 to beread thereby. When a predetermined number of pulses are read, thecounter 33 is reset by the pulse signal I from the pulse amplifier 32.In other words, the counter 33 repeatedly counts a predetermined numberof clock pulses for each pulse period of the pulse signal J. When thecontent S of the reversible counter 30 coincides with the content T ofthe free counter 33, the coincidence circuit 36 provides pulse output K,whereby. the flip-flop 35 provides output signal of waveform L. Thissignal L is smoothed through the d-c signal circuit 37 into a waveformM. Receiving this signal M, the differential amplifier produces outputof an inverse waveform N, which is the difference of the input waveformM from the voltage level for driving the feed motor 28 at full speed.With the voltage of the waveform N the SCR igniting circuit 40 producesa pulse signal 0 which is impressed upon the gate of the SCR 26, so'thatthe output waveform Q of the source transformer 25 is rendered into awaveform P. In this manger, the speed of feed motor 28 is controlled bycontrolling the effective power.

As has been described in the foregoing, according to the invention thespeed of the feed motor is controlled by detecting the relation betweengrinding wheel and workpiece through a detecting circuit, removing noisefrom the detection output to obtain sole spark signal, and modifying thepower supply to the motor according to the spark signal through a speedcontrol circuit. Thus it is possible to achieve continuous control ofthe motor speed at an optimum speed, thus minimizing the wear of thegrinding wheel and improving the precision of machining. Also, since thefeed speed is automatically controlled, the machining efficiency may begreatly increased with the automatic optimum feed of machine table.

What is claimed is:

1. A machine table feed control system for electrolytic grindingmachines comprising a detecting circuit to detect the state of sparkgeneration between a grinding wheel and a workpiece, a spark signalshaping circuit to remove noise from the spark signal output of saiddetecting circuit and shape the resultant spark signal free from noise,a memory to phase modulate the output signal of said spark signalshaping circuit and store the modulated information and a speed controlcircuit to control the speed of a feed motor in accordance with theoutput content of said memory.

2. A machine table feed control system for electrolytic grindingmachines comprising a detecting circuit to detect the state of sparkgeneration between a grinding wheel and a workpiece, said detectingcircuit including a plurality of resonant circuits, a spark signalshaping circuit to remove noise from the spark signal output of saiddetecting circuit and shapethe resultant spark signal free from noise, amemory to phase modulate the output signal of said spark signal shapingcircuit and store the modulated information, and a speed control circuitto control the speed of a feed motor in accordance with the outputcontent of said memory.

i i i i

1. A machine table feed control system for electrolytic grindingmachines comprising a detecting circuit to detect the state of sparkgeneration between a grinding wheel and a workpiece, a spark signalshaping circuit to remove noise from the spark signal output of saiddetecting circuit and shape the resultant spark signal free from noise,a memory to phase modulate the output signal of said spark signalshaping circuit and store the modulated information and a speed controlcircuit to control the speed of a feed motor in accordance with theoutput content of said memory.
 2. A machine table feed control systemfor electrolytic grinding machines comprising a detecting circuit todetect the state of spark generation between a grinding wheel and aworkpiece, said detecting circuit including a plurality of resonantcircuits, a spark signal shaping circuit to remove noise from the sparksignal output of said detecting circuit and shape the resultant sparksignal free from noise, a memory to phase modulate the output signal ofsaid spark signal shaping circuit and store the modulated information,and a speed control circuit to control the speed of a feed motor inaccordance with the output content of said memory.